Cow milk is the most common cause of food allergy in the first year of life, with approximately 2.5% of newborns experiencing allergic reactions to cow milk during this time. The majority of children "outgrow" [become tolerant] their milk allergy in 3-4 years. The most common allergic symptoms involve the skin and gastrointestinal tract. IgE- and non-IgE-mediated mechanisms each appear to account for about one-half of milk hypersensitivity disorders in young children, with the majority of IgE-mediated reactions involving the skin and the majority of cell-mediated reactions involving the gastrointestinal tract. Two forms of IgE-mediated skin reactions have been associated with milk allergy. Acute urticaria is due to allergen-induced cross-linkage of mast cell membrane-bound IgE. Preformed mediators are released, i.e. histamine, leading to localized vasodilation and increased vasopermeability, which results in erythema and edema. Atopic dermatitis also has been associated with IgE-mediated mast cell activation with release of preformed mediators and newly generated cytokines. In addition, cutaneous lymphocyte antigen positive [CLA+] lymphocytes are activated by food allergen ingestion, which probably accounts for the development of the eczematous rash. A variety of cow milk-induced, non-IgE-mediated [presumably cell-mediated] gastrointestinal hypersensitivities have been described. Milk-induced Enterocolitis Syndrome most commonly presents in young infants between 1 week and 6 months of age as protracted vomiting and diarrhea, which not infrequently results in dehydration. Patient with milk-induced Allergic Eosinophilic Gastroenteritis [AEG] generally present with post-prandial nausea and abdominal pain, early satiety or food refusal, vomiting or retching, gastroesophageal reflux and weight loss or failure to thrive. The immunopathology of these two disorders is poorly understood.